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THE PROJECTOR
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design and operation from the disc type. Essentially it is a hollow cylinder of metal, rotating in an end housing.
(81) The Motiograph horizontal shutter is a light aluminum casting rotating on ball bearings and enclosed in a small metal housing. The shutter is positioned transversely (horizontally). In its cylindric stir are two openings through which the light beam passes; the rest of the cylinder serves exactly the same pur]
as the blades of the disc shutter. Its cylindrical diameter is 3.25 inches. Its axis is 4 inches from the projector aperture. See Fig. 115, page 251.
(82) What is true of the speed and width of the disc type master blade edges does not apply to this shutter. and for two reasons : it is located closer to the projector
Fig. 139. — Motiograph Horizontal type rear shutter. This is the shutter used on the mechanism shown in Fig. 115.
aperture and consequently has a smaller beam diameter to cut; the shutter is positioned horizontally, or transversely of the beam, the light passes through its center or cylinder so that when one blade is cutting down through the beam the other is cutting upward, the two interacting at the beam center. Only half the time is required to cut off the light that would be necessary were only one blade in active operation. (83) Of the two blades each acts as a master and cut-off blade.
The Motiograph horizontal rear shutter is shaped at each end of the cylinder to act like a fan or air propeller. From each end air currents are directed toward the center of the cylinder. Each of the two blades of the cylinder has a transverse vane, which, in combina